<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>页面完成加载时显示一个提示框</title>
    <script>
        function mymessage() {
            alert("消息在 onload 事件触发后弹出。");
        }
    </script>
</head>

<body onload="mymessage()">
</body>
</html>